Synthetic tanning agent



Patented June .4, 1946 mosses SYNTHETIC TANNIN AGENT Edwin A. Robinson, Chatha'm,

and Ralph M.

Beach, Fiorham Park, N. .L, assignorsto National Oil Products Company, a corporation of New-Jersey No Drawing. Original application November 21,

. 1941, Serial N 1 v This invention relates in general to the tanning of leather and, more particularly, to new synthetic tanning agents and to an improved Droefls ottanning leather, 1

At'the present time leather is, in the majority oi cases, tanned by either a vegetable tanning process or a chrome tanning process depending upon the type or leather to be produced.

The vegetable tanning process is used principally in -the production of heavy leathers such as sole leather. As the rate of difiusion of vegetable tannin into skin is very slow and, consequently, a long time is required to completely tan heavy leathers with the vegetable tannins, many attempts have been made to speed up this process. One method that has been proposed involves the use of concentrated tanning liquors. However, if hide is put directly into concentrated tanning liquors the rate of combination of the tannin with the skin protein is very likely to be abnormally great compared to the rate of diil'usion of r the tannin into; the interior of'the'skin; consequently. the outer-layers of the hide are drawn or contracted'to a greater extent than the inner layers whereby distortion of the outer layers with respectto inner layers is eilected thus greatly dot flu! from the leather. i

In order to overcome such dimculties, tanners have found it necessary to adopt a stepwise process when' tanning with Vegetable tannins. By

the appearanceand value of 419,944. pllcationAugnst 2, 1945,

'3 Claims. (Cl. 200-124) Divided and this ,ap- Serial No. 608,608

net rofits are much less it would be if a more ei'iicient process were avail able, for producing leather.

The volume of the collagen fibers in the skin increases as more tannin combines therewith and :1 in the manufacture of leather where a great solid ity is required such as, for example; in sole leather.

it is not suiilclent merely to convert all of the collagen into leather but, in order to get the maxi-" the hides, after all of mum fullness and solidity, the collagen has been converted to leather, are

treated with very concentrated tanning liquors so that themaximum .amountor tannin will be fixed. Thusin such cases the prOcess iseVen more cumbersome and costly than that asset out hereinabove. 1

such a process they treat the skins first with a I tan liquor which has already been used to tan a large number oi skins and in which, consequently, the ratio of nontanninto tannin is very great.

At regular intervals the hides are moved into stronger and fresher tanning liquors until they are completely tanned. In some cases, such as in the tanning ofsole leather, months are required to complete the process. Naturally, such a lon drawn out procedure has many disadvantages.

Not only must the tanner have a large amount A of capital tied up in skins which are in the proc- .ess of being tanned but he is also forced to purchase the skins many monthsbefore he will be able to sell them as finished leather. Thus. with the varying market conditionsya great amount of uncertainty and speculation enters into the tanners business. Also, in order to maintain a certain output of leather, he must maintain many times the amount of equipment which he would v a temperature of gelatinization of much over 84 have to have to produce the same amount of leather if the tanning could be accomplished by some shorter and simpler method. Because of these and other inherent disadvantages of the aforementioned procedure, the manufacturers Chrome tanning processes take much less time than vegetable tanning processes and at the pres the world's supply: of light 1 means of chromium salts; 1: of heavy leathers, chrome tanna e will not producethe degree of pluinpness ent time most of. leathers is tanned by However, in the case and fullness which the trade demands. In chrome tanned leathers the individual fibers are usually skin but in vegetable tanned; leathers the fibers are much larger and in most cases they almost completely -fl1l the interilbrillary spaces thus giving a very desirable full and plump a thin as in dried, raw

leather.

Inaddition to the shorter timesrequired for taming bythe chrome processes; such processes also have the advantage of producing leather possessing a much higher temperature of gelatinip zation than can be obtained in leather through 'vegetable tanning. The term .ftemperature-of is used herein to connotevthat which the tanned leather shrinks, or shrivels when subjected to elevatedtemperatures. The temperature of gelatinization is arelative measure or the reaction of the tanning gelatinization temperature at agent upon the skin protein causing the latter to withstand or tolerate various degrees of temperature without harm. Leather properly tanned with chromium salts can usually be kept in boiling water for 5vminutes or longer without show ing any signs of curling. In other words, the leather has, a temperature of gelatinization of C. or higher. However, in. the case of vegetable tanned leathers, it is very diflicult to obtain C. to 86 C. and in many casesthe resulting value is below 84 C.

u Attempts have been made to combine chrome tannage with vegetable tannage. In such cases b v and the cost of the an- 'ished leatherto the consumermuch greater than 1' first-class vegetable tanned the leather is first treated with chrome tanning liquors and then given a surface tannage with vegetable tanning liquors. In some cases and for-some purposes leather which has. been 80 treated is tolerably satisfactory but in many cases and for many purposes it is by no means-as satisfactory as straight vegetable tanned leather.

In viewof the aforementioned-and other various'limitations anddisadvantagesof both chrome and'vegetable tanning and combinations thereof, much'work has been done in attempting-todevelopnew and improved tanning-agents and proc-' cases for using the same. One of-the pioneers in this field was Stiasny who presented to the world a new class of materials which he called syntans." He produced what apparently were condensation products by. mixing and heating phenol sulfonic acids with formaldehyde in an acid solution. He obtained water-soluble products which he claimed possessed marked tanning properties. However, the syntans produced by Stiasny, andsimilar products produced by other investiand ketone groups and, therefore, it isalsoposgators,have had'no fllling'o'r plumping properties and when used for tanning give an-undesirablesthin and empty leather. Moreover, leather producedby the use of such syntans has exhibited a, very poor temperature of 'gelatinization value usually running in the order of about 60 C. to 70* C. as compared to about 80 C. to 86C." for vegetable tanned leather and 100; C. or over for chrome tanned leather.

To increase the temperature'of gelatinization of syntan leather, various investigators have suggested adding chromium salts to the syntans. In

some cases chromic'salts have been added and in some cases chromate compounds but when the chromate salts such as sodium dichromate are added :they invariably reducedto the chromic state with the concurrent oxidation of the syntan, thus producing quinonegroups on the arematicnuclei and converting the methylenic link ages of the condensation" products to carbonyl groups. Inall cases the chromium is apparently present as a positively charged ion, as evidenced As is well known, skin consists principally of protein material which in turn is made up of alpha-amino acids. The alpha-amino acids may be a designated by i the general formula It is known that the hydrogen ofthe carboxyl group tends to shift over to the amino group, leavingthe' carboxyl group with a negative charge and giving the amino group a positive charge, whereby the generalxformula wouldthen be a c coo- I Nae As'chromium is usually present in ten liquors in the form of a positively charged ion, it apparently combines with, the negatively charged carboxyl group. As chromium does form a very stable compound with leather, it seems very likely that ithas chemically combined with the protein in some such manner as we have set out. Invegetable tanningliquors, however, the active tanning agents, according to theProcter-Wilson theory, apparently are negatively charged and thus comvbineiwiththe. positively charged amino groups.-

cf the, skin protein. It is also knownthat vegetable tanning agents contain numerous aldehyde sible that a'chemical combination may be effected between the amino groups of the protein and the aldehyde and carbonyl groups of the vegetable tanning agents in some manner suchas, for examplef In any case, it does seemapparent'thatthe vege-' table tannins combine in some manner with the amino groups of the skin, whereas the chromium in chrome tanning agents probably combines with the carboxyiI'groups of the skin.

In synthetic tanning agents which have been prepared as noted hereinabove by subjectingsulfonated condensation products of phenolic aromatic compounds to oxidation with hexavalent chromium, there are, as already mentioned, both quinone andcarbonyi groups, which may combine with the amino groups of the hide, and. a

positively charged chromium in the trivalent state, which apparently combines with the carboxyl groups of the hide. Since suchi the case it seems possible that this two-fold action tends to draw the different constituent groups ofv the skin more closely together thus causing undesir-' able shriveling and shrinking of the leather. However, whether our theory is correct or not,

it is knownthat the aforesaid synthetic tanning agents have not functioned satisfactorily in leathertanning processes. The use of the'syntan brings about the undesirable result of shrinking the leather.

Since leather having a relatively high temperature of gelatinization can :be'produced andsuch a leather is highly desirable, there is a great demand i'orv a tanning agent whichvmay be usedtto treat leather so that the flnishedleather will not 1 only have the high temperature of gelatinization of chrome tanned leather but also the excellent fullness and solidity of vegetable tanned leather without having the undesired qualities of, leather tanned by either method or by any ofthe various hitherto known synthetic I agents.

There is also "a great demand for a process whereby the time'req'uired for the tanning of leather by vegetable tanning processes may be materially decreased. As aforementioned, in l most cases from two to three months are required to complete the usual vegetable tanning ofheavy I leathers, whereby the processing costs remain exceedingly high.

Itis the object of this foregoing and other disadvantages inherent in the tanning of leather.

It is also the object of this invention to. provide new and improved synthetic tanning agents. A further object of the invention is to provide improved synthetic tanning. agents which will 1| produce leather which is Plump and soft and invention to obviate and a high tempera- Other object of the invention will in part be obvious and will in part appear hereinaftert.

It has now been found that the foregoing and other objects of the invention maybe accomplished by treating a sulfonatedlignin compound with a compound containing hexavalent chromium in such a manner that the chromium, or the major part thereof, will be reduced to trivalent chromium, but so regulating. the conditions and quantities of materials thatinstead of chromium being present in the finished product in the form of a positively charged ion, it will be present in a negatively charged complex ion; and by using tanning agents so produced in a manner as set out hereinafter.

According to Werners coordination theory as set out in his book "Neure Anschauungen auf dem Cebiete der Anorganischen Chemie, certain atoms tend to draw to themselves, in the form of surrounding shells and by forces'other than primary valence, a number of other atoms or coordinated groups. The central atom with its coordinated groups constitutes a nucleus outside of which are located the atoms or radicals which are held to the rest of the molecule by primary valence forces. The coordination'number of an element indicates the number of groups which an atom can hold in this, surrounding shell. Chromium happens to boom of the metals whose atoms have this; power to combine with other atoms not only by means of their recognized primary valence forces butalso bymeans of these so-called auxiliary valences. The majority of metals, including chromium, have acoordination number of six.

This property ofcertain elements to form such complex ions containing coordinately bound atoms or groups may be illustrated by structural formulae of three different forms of chromic chloride. The alpha form of chromic chloride is a violet salt of the formula C1C13.6H2O. All of its chlorine atoms are precipitated from solution by the additionof silver nitrate and, according to Werner's theory, its structural formula is:

H10 Or H 301- H 0. 1110 in this state'they arereadiiy precipitatable by silver ions. r I I The beta form of chromic chloride is a green salt of the formula CrC1:.5H20. Only two-thirds of its chlorine is precipitated from solution by silver nitrate which indicates that only'two of the chlorine atoms are bound to the chromium nucleus by primary valence forces and that the third is now contained within the nucleus. Thus the formula would be:

' mo or mo :01-

mo c1.

When the one chloride ion penetrates into nucleus it displaces one of the water molecules and as the chloride ion is negatively charged it neutralizes one of the three positive charges on the nucleus. When it does this. the chloride ion ceases to be an ion any longer but now forms part of the complex which constitutes the nu cleus, and it is incapable of being precipitated I by silver ion.

' ride ion is left capable of In the gamma form of chromic chloride, two

chloride ions have penetrated into the nucleus, thus displacing two of the coordinately bound water molecules to give the formula CrCh.'4HaO which may be depicted structurally as follows:

come a part of the nucleus. The nucleus now has only one. positive charge, and only on ch10- precipitation by silver nitrate. v v i By suitably varying the conditions, it is possible to replace all of the coordinately bound water molecules with chloride ions andthus obtain a nucleus having three negative. charges. Thus, for example, it is possible to obtain a chromium compound such as sodium hexachlorochromia't'e ,whose structural formula would be:

C! Cr Thus the chromium is now present in 'a 'nega tively charged complex ion and all of thechlorlne atoms are attached to the central chromium atom by nonionized links.

.The chlorides of chromium havebeenused here merely to illustrate Werner'fs theory. Chloride ions are not the only ions that may penetrate into the nucleus; a great many other atoms or radicals will also penetrate into the nucleus and become bound by nonionized links. In fact, even molecules may do this as we have already seen in the case of the hydrated chromic chlorides where molecules offlwater arecontained in the nucleus. When charged ions or radicals f penetrate into the nucleus, they either increase the positive charge or decrease the negative charge, or decrease the positive charge or increase the negativecharge of the nucleus depending upon whether the. nucleus is originally positively or negatively charged and whether the ion or radical penetrating, into the nucleus is positively or negatively charged, respectively.

We have found that by treating "sulfonated lignin compounds with hexavalent chromium in such a manner that. the sulfonated compound will be partially. oxidized, and the hexavalent chromium reduced to trivalent chromium, and negatively charged complex chromium ions "formed instead of positively charged chromium as is usually the case, very efllcient tanning agents result which when used to tan'hides will produce a very desirable leather. it hides are given a Dretan with such, tanning agents, they'may then be treated immediately with concentrated tanning liquors, whereby vege- Furthermor';

accuses" v I table tanned leather of very high quality is produced. By such a process vegetable tanned heavyJeather can now be produced in iromj to 12 days. 'Moreover, the leather resulting from this process is far-superior to that produced in from 60 to 90 days ,bythe ordinaryknown vegeaccording to our invention, no precipitate of chromium hydroxide is obtained. 7

Wehave found that in order to obtain the desired chromiate ions-much less dichromate must table tanning methods. addition totheshorter length or time requirediorthe tanning and the leather having all the desirable qualities of the vegetable tanned leather, the leather a -n! of the ish r' i a e qualibe used than is used inthe-aforesaid German patent} In determining the amount o! dichromate to use in treating the solids. obtained from. waste salute-liquors, it has been found to be moreyconvenient to ,calculate theamounts on a percentage rather than to attempt to use a mol basis. In" order to obtain the desiredprodties or chrome leather. e.-kg., amen-um.

perature of gelatinizatiom ur vcntiqhli invention, i y es-ma vi hg a mld hv much as; acted i f r elash d rm s con sa n tresultins products then treatedwithhexavalentchromiumcontaining compoundflii'sodesired. h s;

' mlxsuitable hexavhlent c 'ucts, we have found it best not to use over about of sodium'dichromate on the basis'oi the total solids .in'the waste sulflte liquors, and

preierto'useabout 12% to 14% 0t dichromate based onthe' total solids in the liquors. However,

- even'smaller'amounts of dichromate feral v.a' iri-,i {sulfuric acid being preferred, reterably usi'nsqfrom to or more of.

,acidfon the basis or the total solids in the waste 7 1iquors,- although amounts as ;low as 20% may be used. When carrying out thedichromate treatment, it is preferred thatthe wastesulnteliquors compound may be le tdtreat the s'ulionated 11mm comp undsaltnmh. o t' courde. mor convenient tormsfsneh as-cod-ium' dichromat'e'and potassium dichromate are highly preferred.

order. to;produce;2the synthetic tanning agent's or omwnivention; it is veryimportant that the conditionsunderi which they are prepared be carefully and-that the-proper proportions'of mqteriaisbe v I,

weaareaware-of Gex-man Patent No. 664,086 and its disclosure dealing with the treatment of sultite cellulose liquors with ehromate or bichromate in gsucha manner that non-tanning I tillers in the 'sulflte cellulose waste liquors serve to convert 'theg-hexavalentchromium to trivalent 011 10 1 1 1 with concurrent oxidation of the nontanning the process-disclosed in this patent, the liquors I are lust' as they re o t ln d;-fmmj the...cellulosefvboiloir, rather than in a -:soniewhat,;;conccntii d I term. Such waste liquorscontainj onlyragsmall percentage of utotai'f solids. Inregard topthe. actual content or total solids ot such liquors', it is stated in The Manufacture or Pulp and Paper," vol 3, 3rd edition, section 4, p. 95,.that 'the-so1ids represent only llto 12 per cent oi thetotal liquor." Thererore in; the single example which isgiven in the patent, the patentees I have usedapproximately three partsot fsodium vbichromate for-every two parts of solids. id-the waste sulnteliquor. Such contain 50% or more water. The upper limit or the amount of water in'the sulfite liquors will depend of course on how concentrated itis'de-V siredto have the final product. If desired',;1-the waste sulfite liquor solids may be obtained inthe dried Iorm and usedin producing the products of our invention. In such a case it will be necessary to add water to the dried solids before treat ing them with the dichromate.-

In neutralizing the excess sulfuric must be taken to add the alkali slowly and; with stirring in order to prevent the rormation' goi-g lumpy particles in the mass. It is preferred-to use from a 15% to a 30% NaOH solution to neutralize the excess acid,although other bases may be-used if so desired. Enough alkali is added so that a 2% aqueous solution of the end product will have a pH between about 3 and 6. r

The products of our invention may be used in the tanning of leather just as other tanning agents are used. They' are particularly applicable, however, to the pretanning of heavy leather such as sole leather. Leather pretreated in this manner can then be vegetable tanned in from 10 to 12 days whereas, ordinarily, several months would be required to give the heavy leathers a an amountoi'g-chromate isJe'nti'i-eIyZ-toO much to produce the iproductswhichfwe obtain by our invention. .I'he-patentes saythat their final prodnot is completely firee oichromate ion and has exchangeditsjoriginal brown color for the green of the trivalant. chromium, which indicates that the o -is present as the positively c a p" trivalent .ion.-- Solutions of our products are usually of a reddishbrown color.

We prepared products according to the process set'out in the one example given in me German;

patent and found that the chromium was in fact present 'as the positively charged ion since when an exces of caustic alkali was added to solutionsof the products, a precipitate of chromium hydroxide was obtained. -When an excess oi' caustic alkali is added to solutions of the products produced from the solids'in waste sulflte liquor complete vegetable tannage. timum penetration of the syntans into the hides,

the pH of the tanning liquor should preferably be between about 4 and about 5. Also, it is preferred that the concentration of the tanning liquor, when-the leather is tanned in drums, be

such that it contains at least 6% of syntan solids. I

The presence of neutral mineral salts, such as sodium chloride, sodium sulfate, potassium sulfate, etc., will also assist the penetration of the syntans into the hides.

chloride, a concentration of 0.5% (based on the In the case of sodium weight of the tanning liquor solution) has given i very goodresults; however, even smaller amounts will materially aid the penetration of. the syntans.

The pH of the tanning liquors should not be much les than 3, nor much greater than 5.

Because of theavailability and. relative'inex- .pensiveness of waste sulflte liquors, our products produced by treating waste sulflte liquors form the preferred embodiment of our invention. Either the waste suliite liquors as such or the commercially available concentrated liquors conmaybe used.

. tore treating the waste sulfite liquors with "theidichromate, they are acidified with asultable To obtain an 011-: v V

'taining about 50% water may be used. Also, ii. desired, the dried solids of the liquors may be used, in which case they are dissolved in water before being used. Itis immaterial whether the lignin sulfonic acids in the liquors are present in the free acid form or as alkalimetal salts as either form may be employed in accordance with our invention.

For a fuller understanding of the nature and objects of the invention, reference should be had to the following examples which are given merely to further illustrate'the invention and are not to be construed in a limiting sense, all parts given being by weight: c

a Example 1 Waste sulfite' liquors containing about 50% water were acidified with sulfuric acid and then treatedwith a solution of sodium dichromate (about NazCr2O-1 on the weight of the sulfite liquor). Q'Iheaddition of the dichromate was made slowly, while cooling. The mixture was allowedtd'stand overnight at room temperature and thenthe mineral acid was neutralized with caustic soda and the product adjusted to a suitable pH. This product. was used to-tan raw kid skin. The leather. produced was well filled and had 1 a temperature of gelatinization of over 100C.

i Example II 50 parts of dried solids obtained from waste sulfite liquors were mixed with 400 parts of water and 25 parts of sulfuric acid and treated much the sameas the waste sulflte-liquors in Example 'I with 9 parts of sodium dichromate in a 50% solution. 'lhe product was neutralized with soda and adiusted to the desired pH.

10 parts by weight on the total solids basis of th product were added to. 100 parts of water and the resulting tanning, liquor used to tan 100 partsof pickled kid stock by drumming at room temperature for six days. The leather was then removed, washed, fat-liquored and dried. A very good quality leather having a temperature of gelatinization of over 100 C. was obtained.

- Example [11 A tanning agent was prepared from dried solids obtained from waste II, except that 20 parts of formalin (37% formaldehydei wereaddedto the waste sulfite liquors and the n'ixture was allowed to stand overnight before the treatment with dichromate.

Pickled kid skin was tanned with the resulting product as in Example II and equally good results were obtained.

Example IV 400 parts of concentrated waste sulfiteliquors containing about 50% water were acidified with 60 parts of sulfuric acid and then treated with 49 parts 01' a 50% The dichromate was solution of Na2Cr2O72I-I2O. added at about room temperature and the mixture then warmed to about Example V 40 lbs. of one of the synthetic tanning agents of the invention were made up to 17.5 gallons with water and adjusted to the proper pH. The resulting tanning liquor and 145 lbs. of hides were sulflte liquors as in Example placed in a drum and run for six hours. The wheel was .then stopped for two hours'and'then turned on for one-half hour every two hoursfor twenty-four hours. (Constant running-creates too much heat.) After this pretanning, the hides were vegetable tanned in the usual manner. Much less time was required to completely vegetable tan the leather than in the case of hides not pretanned with one 'of the synthetic tanning agents of the invention.

Example VI Much less time is required to complete the process thanwith the usual vegetable tanning methods.

Use a slow running drum, about sixto eight R. P. M. Place in this drum a short liquor consisting of one pound of solution for each pound of bated stock. This solution should-be so made up that itcontains 10% of syntan solids based on bated stock weight. The stock should be run in this solution for 24 hours using a procedure such that the 'mill is run thirty minutes each two. and one-half hour period, afterwhich the solution should be drained from the mill." Next use a long vegetable tan liquor made up-of a tail rocker liquor and run intermittently for 24 hours; then run tail liquor to sewer. V

The semitanned hides arethen run until struck through in a short vegetable tan liquors-having an barometer strength, using for-this solution a blend of tan materials in layaways or extract wheels.

, This run should be intermittent as in the. previous steps, afterwhich the hides can be wrung, and are then ready bleaching,

for the usual extracting, tempering, loading and finishing procedure. 1

From the above examples and description-it can readily be seen that we hav produced-novel synthetic tanning agents. These syntans appar-- ently contain. chromium in the form of a nega --They appar-' J .ently react with the skin collagen to form'leather.

in much the same way as vegetable tanning desirable fea tively charged ion or chromiate.

agents. Not only do they have the tures of vegetable tanning agents but also those of chrome tanning agents and thus they are well adapted to tanning various types of leather..; Inaddition, they are excellent pretanning agents and heavy leather which has been pretanned with them may be given a complete vegetable tannage in from ten to twelve days, whereas: several months would ordinarily be required for usual vegetable tanning.

The exact chemical structure of the tanning agents or the exact mechanism by which they are formed has not as yet been definitely determined. However, we believe that negatively charged constituent groups or possibly a whole molecule of sulfonated material bearing a. negative charge penetrates into the chromium nucleus, thus giving it a negative charge as a result of which the chromium will not be precipitated when excess alkali is added to the product. However, it is possible that the negative charge may not be due entirely to the sulfonated aromatic compounds or the condensation products thereof since the reaction is carried out in the presence of a mineral acid, preferably sulfuric acid, and acidic radicals may thus penetrate into the chromium nucleus and contribute to producing the negative charge thereon. Furthermore, the

similar to thatused' hydroxide is used to neutralize the reaction mass,

the syntans have the following general formula:

soi). (nlo).-di-(L.sol), x).

wherein Cr stands for trivalent chromium, L.SO3

represents lignin sulfonateor a formaldehyde condensation product thereof, m represents a wholemumber of through 2, n represents "a whole number of 1 through 3, q stands for a whole number of 0- through 2, represents a whole number of 1 through 6, and X represents apositive monovalent salt-forming element or group. A covalency of ,6 for the chromium atom will obviously call for the following algebraic relations between m, p, q, and n:

. Whenever p is more than 1, L503 may represent both lignin sulfonates and formaldehyde concourse, if some mineral acid other than sulfuric acid, e.;g., hydrochloric acid, is used in the process, the S04 groups in the general formula may be replaced by other acidic groups or ions, e. g., chloride ions. Since, however, waste sulflte liquorscontains sodium sulfate, there may be sulfate groups in the complex "chromiate ion even when sulfuric acid is not used in the reaction. If lignin sulfonate, part of which has been condensed with formaldehyde, is reacted according totheprocess of our invention with sodium dichromate in the presence of sulfuric acid and the reaction mass neutralized with a sodium alkaline agent such as sodium hydroxide, synthetic tanning agents maybe obtained having a formula such as one of the following:

(Formaldehyde condensation product of lignin sullonateh .2Na+

or v

(Lignln Sultanate): E

(Formaldehyde condensation product of lignin sulfonate): .3Na+

Of course there are many variations ofthegeneral formula given above which may be formed.- .Large and complex molecules may thus be built up and give thefsyntans the. filling-properties which are desired. It is also known that under certain conditions two or morechromium nuclei containing coordinately bound atoms or. mole.- cules may unite and thus formstill larger'com pounds. This is known as olificationf and it is very possible that such may be taking place in the formation of our tanning agents and may partly be the reason for their desirable filling properties. v i

Since certain changes in carrying out the above process and certain modifications in the com position which embody the invention may be made without departing from its scope, it is intended that all matter contained in the above description shall L be interpreted as illustrative f and not in a limiting sense. i 1" This application is a division of our application Serial No.'419,944, filed November 21, 1941.

Having described our invention, what we claim as new and desire to secure by Letters Patent is:

1. A process of producing novel chromiates having tanning properties which comprises reacting a water-soluble dichromate with a lignin sulfonic acid-formaldehyde condensation product, the quantity of dichromate used being not morethan 20% based on the weight of the solids in the" lignin sulfonlc acid-formaldehyde condensation product. v 2; The process of claim 1 wherein the quantity of dichromate used is within the range of 12% to 14% based on the weight of the solids in the lignin sulfonic acid-formaldehyde condensation product. ,7

3; The product of the process of claim 1.] EDWIN A. ROBINSONLQ RALPH M. BEACH. 

